1. Field of the Invention
The present invention relates to a resist composition which causes reaction upon irradiation with an actinic ray or radiation to undergo change in the properties thereof, and to a pattern-forming method using the resist composition. More particularly, it relates to a resist composition which can be used in the step of producing semiconductors such as ICs, producing circuit substrates for liquid crystal or thermal head, or in other photo fabrication steps, and to a pattern-forming method using the resist composition.
2. Description of the Related Art
A chemically amplified resist composition is a pattern-forming material which generates an acid in exposed areas upon irradiation with an actinic ray such as UV rays or radiation, causes change in solubility for a developer between irradiated areas and non-irradiated areas, and forms a pattern on a substrate.
In the case of using a KrF excimer laser as a light source for exposure, compositions mainly comprising a resin having a fundamental skeleton of poly(hydroxystyrene) which is small in absorption in wavelength region of 248 nm are used. Such system provides high sensitivity and high resolution and forms a good pattern, thus being a better system as compared with those wherein conventional naphthoquinonediazide/novolak series resins are used.
On the other hand, in the case of using light sources having further shorter wavelength, e.g., an ArF excimer laser (193 nm), there have been developed resists for the ArF excimer laser which contain a highly transparent resin having an alicyclic hydrocarbon structure, because compounds having an aromatic group essentially have large absorption in wavelength region of 193 nm.
JP-A-2002-372784, JP-A-2004-12545 and JP-A-2003-5374 disclose resist compositions using a plurality of resins in order to improve such performances as sensitivity, iso/dense bias, etching resistance, and defocus latitude.
In view of total performance as a resist, it is extremely difficult, as things stand, to find out an appropriate combination of resins, photo acid generators, additives, solvents, etc. to be used. Further, upon formation of a fine pattern of 100 nm or less in line width, it has been demanded to solve the problem of pattern collapse which leads to defects upon production of devices, to improve line edge roughness of a line pattern, and to improve four performance factors of pattern collapse, line edge roughness, exposure latitude (EL) showing degree of fluctuation of a pattern dimension due to change in exposure amount and defocus latitude (DOF) with good balance.
The term “line edge roughness” as used herein means that the edge of the interface between a line pattern of a resist and a substrate has a form irregularly fluctuating in the direction vertical to the line direction. When this pattern is viewed from just above, the edge seems uneven (with an unevenness of from about ±several nm to about ±several ten nm). Since this unevenness is transferred to a substrate in the etching step, a large unevenness would cause electrical characteristics failure, which results in reduction in yield.
In the invention, particular attention is paid on living radical polymerization which can narrow or reduce a molecular weight distribution (degree of dispersion) noting uniformity of the resulting polymer. The term “molecular weight distribution” as used herein means the ratio of weight-average molecular weight to number-average molecular weight. A ratio nearer to 1 means a narrower molecular weight distribution. So far, JP-T-2000-515181 discloses a process for synthesizing a polymer by living radical polymerization. In addition, JP-A-2005-156726 discloses a resist composition using a polymer obtained by living radical polymerization which, however, cannot be said to provide sufficient resist performance.